Polymer blends which have a combination of both, thermoplastic and elastic properties (thermoplastic elastomers, TPE) are generally obtained by blending a thermoplastic polyolefin with an elastomeric composition (rubber) in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized compositions is found in U.S. Pat. No. 3,037,954 to Gessler which discloses static vulcanization as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composition (thermoplastic elastomer vulcanizate "TPV") is a microgel dispersion of cured elastomer, such as butyl rubber, chlorinated butyl rubber, polybutadiene or polyisobutene in an uncured matrix of thermoplastic polymer such as polypropylene. Since then the technology has advanced significantly.
U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber such as, inter alia, butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene.
U.S. Pat. Nos. 3,758,643 and 3,806,558 disclose polymer blends comprising an olefin thermoplastic resin and an olefin copolymer rubber wherein the rubber is dynamically cured to a partial cure state. The compositions can be reprocessed, however, the potential applications of such blends are limited by their high compression set and/or low softening temperature resulting from only a partial cure of the rubber. Furthermore, the partial peroxide cure utilized in such blends is difficult to control from the standpoint of completeness of reaction, resulting in batch to batch variations in product properties.
Japanese Patent Application 85,530/87 discloses a DVA composition including a crystalline polypropylene as a matrix and two elastomers: a bromobutyl rubber and an olefin copolymer rubber such as EPM or EPDM rubber.
U.S. Pat. No. 4,130,5334 discloses elastoplastic compositions comprising blends of cross-linked butyl rubber and a thermoplastic polyolefin resin. The blends disclosed comprise about 20 to 45 parts by weight of the thermoplastic crystalline polyolefin resin and from 80 to 55 parts by weight of butyl rubber, chlorobutyl rubber or bromobutyl rubber, per 100 weight parts of polyolefin and rubber.
U.S. Pat. No. 4,810,752 discloses a thermoplastic elastomer composition comprising a halobutyl rubber which is cured in the presence of a mixture of a polyolefin and a thermoplastic elastomeric block copolymer such as SIS, SEBS or SBS.
U.S. Pat. No. 4,916,180 discloses a thermoplastic elastomer composition comprising a butyl terpolymer rubber and polypropylene. The rubber is cured with a peroxide curing agent. Said butyl terpolymer comprises a major portion of isobutylene, a major portion of isoprene and a minor portion of a divinyl aromatic monomer of the formula R--CR.dbd.CR--X--CR.dbd.CR--R in which X is an aromatic nucleus and R is independently selected from hydrogen or C.sub.1-5 alkyl.
European patent application 0 320 263 (published on Jun 14, 1989) discloses the introduction of branching into C.sub.4 to C.sub.7 isoolefin homopolymer rubber, butyl copolymer rubber, halogenated copolymer rubber (C.sub.4 to C.sub.7 isoolefin/C.sub.4 to C.sub.14 -conjugated diene), and mixtures thereof by reaction with a functional agent, i.e., a branching agent for the purpose of modifying the molecular weight distribution. The modification of the molecular weight distribution of said rubbers is achieved by incorporating during polymerization of the polymers an effective amount of a functional reagent selected from the group consisting of polymers and copolymers comprising functional groups capable of copolymerizing or forming a chemical bond with the product polymer, the functional group comprising cationically active halogen or cationically active unsaturation and such polymers and copolymers preferably comprising lyophilic polymerization diluent soluble moiety. The copolymers thus obtained are called "star-branched copolymer rubbers" or "star-branched butyl rubbers" and may be halogenated.
U.S. Pat. No. 5,286,804 and the International Patent Application Publication WO 91/13102 disclose an improved process for halogenating star-branched butyl rubbers.
The thermoplastic elastomer vulcanizates based on butyl and halogenated butyl rubbers known in the art, however, show limitations with respect to the balance of physical properties (tensile strength, elongation at break) and processability, i.e., allowing to obtain shaped articles after injection-molding, extrusion and blow-molding which show no defect, such as on the surface, at the edges, etc. Also the manufacturing process of these butyl and halogenated butyl rubber based thermoplastic elastomers has been found to be difficult and complicated and requires intensive mixing.
It is an object of the present invention to provide curable composition which comprises a thermoplastic polyolefin resin and a rubber which can be converted into a thermoplastic elastomer vulcanizate which has an improved balance of physical properties and superior processability. In detail it is an object of the present invention to provide a thermoplastic elastomer based on not only butyl but also halogenated derivatives which is easy to be manufactured and easy to be processed using all the processing devices like extrusion, injection molding, blow molding, etc. with excellent articles aspects.